Template-free Synthesis Of Ce-Zr Based Catalyst With Hierarchical Pore For VOCs Removal

VOCs are capable of undergoing photochemcial reactions with NOx to form huge amounts of photochemical oxidants which are responsible for the formation of haze. They are considered as great threats to human beings' health and environment. Catalytic oxidation has been identified as one of the most effective and versatile techniques used for destructive removal of low concentration of VOCs. The catalytic performance of catalysts is the most important factor to determine the process being economic and efficient.In this study,the CuCe0.75Zr0.25Oy mixed oxide catalysts and the supported CuCe0.75Zr0.25Oy/H-ZSM-5 catalysts were prepared by different methods. The physical and chemical properties of the catalysts were investigated by using XRD, N2 adsorption-desorption, H2-TPR,NH3-TPD,O2-TPD and Raman. Catalytic performances for toluene and/or ethyl acetate oxidation over these catalysts were tested in a fixed-bed reactor in order to explore the relationship between the catalytic activity and the physico-chemical properties of the catalysts.(1) Catalyst activity and structure can be greatly influenced by the preparation methods. The CuCe0.75Zr0.25Oy catalysts were prepared by sol-gel,thermal decomposition,solid state reaction, and the CuCe0.75Zr0.25Oy/H-ZSM-5 catalysts were prepared by saturated impregnation and incipient wetness impregnation methods. It was concluded that the surface area of the supported catalyst was the one of the favorable factors for toluene abatement, however, the effect of surface area on the activity of the mixed oxides catalyst could be ignored. The negative influence of the bulk CuO presented in the catalyst on its activity was obtained which could be attributed to decreasing of the synergetic effect between CuO and CeO2. The CuCe0.75Zr0.25Oy catalyst prepared by sol-gel method possessed more excellent catalytic activity than that of the catalysts prepared by other methods, which T10,T50 and T90 were 137?,183? and 219?, respectively.Low-temperature reducibility and rich lattice oxygen resulted in the highest activity of the CuCe0.75Zr0.25Oy catalyst, simultaneously, the larger pore sizes were also beneficial to the migration and diffusion of reactants and products. And no deactivation was observed during the 72 h stability test at 300 ? which was higher than T100 (260 ?).(2) Pore former is one of the key factors that influences the catalyst activity. The effects of biological-pore formers (bacterial cellulose, BC in short) and the chemical pore formers (oxalic acid, citric acid and the mixture solution of oxalic acid with cyclohexane or ethylene glycol) on the CuCe0.75Zr0.25Oy catalyst activity were investigated. It can be obtained that the CuCe0.75Zr0.25Oy catalyst prepared by the sol-gel method using the BC pore former presented the highest activity for the toluene removal, and its T100 was as low as 220 ?, it is worth noting that T100 is much lower than those of the other catalysts. The excellent activity of the CuCe0.75Zr0.25Oy catalyst should be attributed to hierarchical pores structure and the more relative concentration of oxygen vacancies.(3) The CuCe0.75Zr0.25Oy catalyst prepared by the commercial BC (Com-BC) showed better activity than that of the catalyst prepared by the cultured BC (Com-BC). The T100 of the Com-BC catalyst for toluene and ethyl acetate were 220 ? and 170 ?,respectively,which were 20 ? and 30 ? lower than those of the Cul-BC catalyst. No deactivation was observed during the 100 h stability test for toluene and ethyl acetate oxidation at the temperature of their T100. The hierarchical pores structure with micropore, mesopore and macropore, the higher dispelrsion and samller average crystallite size of CuO resulted in the the excellent activity of the Com-BC catalyst.